Novel nanoparticles change color

Engineers at Ohio State University have invented nanoparticles
that, somewhat unusually, glow red, green or yellow depending upon the state of
the quantum dots contained within.

This series of photos depicts a novel nanoparticle changing from
red to green to yellow over the course of 2 min. Courtesy of G. Ruan, Ohio State
University.
Researchers routinely tag molecules with fluorescent materials
to see them under the microscope. Unlike the more common fluorescent molecules,
quantum dots shine brightly and could illuminate chemical reactions especially well,
allowing researchers to see the inner workings of living cells. The new nanoparticles
could be a useful addition to the arsenal of biomedical engineers trying to find
the roots of diseases, scientists said.

“This work could be groundbreaking for the field of nanotechnology
as a whole because it solves two seemingly irreconcilable problems with using quantum
dots,” said research scientist Gang Ruan.

Because of their quantum mechanical effects, quantum dots “twinkle”:
They randomly blink on and off. When many dots come together, however, the blinking
becomes less noticeable – and when large clusters form, they appear to glow
with a steady light. Researchers have found the blinking in quantum dots to be troublesome
because it interrupts a tagged molecule’s trajectory when they are trying
to follow it. But blinking is beneficial too because, when dots come together and
the blinking disappears, they know that tagged molecules have aggregated.

The scientists discovered that they could use the “good”
and avoid the “bad” aspects of blinking by grouping together a few quantum
dots of different colors inside a micelle – a nanosize spherical container
found in household detergents. Ruan and his team created micelles from polymers,
with various combinations of red and green quantum dots inside.

Experiments confirmed that the micelles appeared to glow steadily.
Those stuffed with only red quantum dots glowed red, and those stuffed with green
glowed green. However, those stuffed with red and green dots changed from red to
green to yellow. The color changes occurred when one dot or another blinked inside
the micelle. Much as with the single-color-stuffed micelles, the dual-color-stuffed
micelles could blink solely red or green – but if both lit up simultaneously,
the micelle glowed yellow from the additive effect.

It’s not possible to control when color changes happen inside
individual micelles, but the continuous glow allows uninterrupted tracking of tagged
molecules, and color changes indicate when molecules have come together. The particles
also could be used in fluid mechanics research, the scientists said.

The team also is working on developing magnetic particles to enhance
medical imaging of cancer, which, combined with the quantum dot technology, could
enable various types of imaging methods. Before the particles could be safe to use
in the body, however, they would have to be made of biocompatible materials.

In the future, the scientists hope to introduce another color – blue – into the mix to see what happens.

An instrument consisting essentially of a tube 160 mm long, with an objective lens at the distant end and an eyepiece at the near end. The objective forms a real aerial image of the object in the focal plane of the eyepiece where it is observed by the eye. The overall magnifying power is equal to the linear magnification of the objective multiplied by the magnifying power of the eyepiece. The eyepiece can be replaced by a film to photograph the primary image, or a positive or negative relay...

The use of atoms, molecules and molecular-scale structures to enhance existing technology and develop new materials and devices. The goal of this technology is to manipulate atomic and molecular particles to create devices that are thousands of times smaller and faster than those of the current microtechnologies.

Also known as QDs. Nanocrystals of semiconductor materials that fluoresce when excited by external light sources, primarily in narrow visible and near-infrared regions; they are commonly used as alternatives to organic dyes.